The present invention relates to the graphical display of data. More specifically, the invention relates to the display of chromatographic separation data that are a series of measurements over time in a graphical format, e.g., as a series of bands.
Analysis of biological samples often requires the resolution and characterization of the constituent elements of the sample. The more interesting of these constituents are macromolecular structures, e.g., proteins, nucleic acids, carbohydrates, and the like. Typically, analytical separation of macromolecular species is carried out using chromatographic techniques. Of particular widespread use are electrophoretic techniques that employ slab-gels disposed between two glass plates as a separation matrix. Samples containing the macromolecular species that are sought to be analyzed, are introduced into wells at one end of the slab gel. An electric current is then applied through the gel drawing the macromolecular species through the gel by virtue of a charge either on, or otherwise associated with the macromolecular species. Each sample travels through the gel substantially linearly, e.g., in a lane corresponding to its well.
As the sample progresses through the gel, molecules of different size and/or charge will have different mobilities through the gel, and will separate into bands that reflect their relative size and/or charge. Upon completion, the gel is stained or otherwise examined whereby the various bands can be visualized and compared with standard macromolecular compounds, e.g., having standard molecular weight and/or charge, e.g., isolectric point.
For example, in the case of protein analysis using sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE), proteins are drawn through the gel matrix in a highly charged detergent micelle (SDS) to ensure that the proteins, regardless of charge, will electrophorese through the gel. The proteins will travel at a rate that is proportional to their size. Once separated, the protein bands are stained, e.g., with coomassie blue or silver staining, to permit analysis and recordation, e.g., as a photograph or a digital or analog scan.
Similarly, nucleic acid analyses utilize a similar gel system, e.g., agarose or polyacrylamide gel. Upon application of a current through the gel, the nucleic acid samples, again disposed in wells at one end (anode) of the gel, will electrophorese through the gel. The polymer gel presents a sieving matrix, where larger nucleic acid fragments that otherwise having the same charge: `mass ratio as smaller fragments, will travel more slowly through the gel than the smaller fragments. Upon completion of electrophoresis, the lanes of samples are analyzed for the pattern of the bands (or xe2x80x9cladderxe2x80x9d as it is often termed). Analysis of the bands may be carried out by adding a fluorescent intercalating agent to the gel, or by incorporating a radioactive label within the nucleic acid fragments, followed by contacting the gel with a photographic film.
Typically, electrophoresis gels run multiple samples within the same slab gel along with one or more standards or markers, which are used to characterize the sample constituents. For example, in size-based separations, standards typically have a range of known molecular weights. Sample constituents are then compared to the standards to determine their molecular weights, e.g., by interpolation. Such standards must generally be run in the same gel as the sample, in order to provide assurances that the standard was subject to the same separation conditions, e.g., gel composition, electric current, temperature, or other parameters affecting separations.
Despite the efficacy of these slab gel electrophoresis, however, such methods are quickly being supplanted by automated procedures that generate a stream of digital data. This data, in its raw form, may exhibit the non-linearities described earlier, or different ones, or none at all. Such data may be generated, for example, by passing a sample in front of a sensor. Alternatively, it is also possible to digitize the raw information presented in a traditional gel by scanning it to produce a series of measurements. The display of such information is not provided by current systems.
What is therefore needed are techniques for displaying chromatographic separation data that are a series of measurements over time in a format similar to that of traditional gel presentations. Moreover, it would be beneficial to provide normalization of such data, if desired.
The present invention provides innovative techniques for displaying a series of measurements, e.g., as acquired from a microfluidic capillary separation experiment, in a gel-like format. This gel-like format displays chromatographically separated and detected species as bands of varying width and intensity in a vertical lane format, e.g., as a ladder. This format further permits the side-by-side display of chromatographic data from multiple different samples, which data can be normalized to internal standards. In particular, chromatographic data obtained in the form of optical intensity, e.g., fluorescence, UV absorbance, or the like, as a function of time, e.g., as a chromatogram, can be displayed in a band format, as a ladder. Further, serially acquired data from analysis of multiple samples, e.g., from serial separations in the same separation system, as opposed to parallel acquired data, e.g., from a multi-lane slab gel, can be displayed side-by-side, and can be normalized to one or more standards.
In one embodiment, the invention provides a computer implemented method of displaying chromatographic separation data. A series of measurements indicating presence of constituents in a sample at a scanning location over time is received. The series of measurements for the sample is displayed as a series of bands. Additionally, peaks in the series of measurements can be identified that correspond to one or more markers. The series of measurements can be scaled so that any displayed bands that correspond to the one or more markers are aligned with predetermined locations or markers from a previous or the same sample.
In another embodiment, the invention provides a computer implemented method of displaying chromatographic separation data. A series of measurements indicating the presence of constituents and at least one marker in a first sample at a scanning location over time is received. A series of measurements indicating the presence of constituents and at least one marker in a second sample at a scanning location over time is also received. The series of measurements for the first sample is displayed as a series of bands. The series of measurements for the first sample is analyzed to identify at least one peak that corresponds to the at least one marker. Similarly, the series of measurements for the second sample is analyzed to identify at least one peak that corresponds to the at least one marker. The series of measurements for the second sample are scaled so that the displayed bands that correspond to the at least one marker in the first and second samples are aligned when displayed. Lastly, the series of measurements for the second sample is displayed as a series of bands adjacent to the bands for the first sample.
In another embodiment, the invention provides a computer implemented method of graphically presenting chromatographic separation data. Chromatographic data for a sample is acquired, the chromatographic data for the sample including a set of constituents and a set of markers. A position of each marker in the chromatographic data is determined in order to define a range of positions. Additionally, an intensity of each marker in the chromatographic data is determined in order to define a range of intensities. The position of each constituent in the chromatographic data is determined by scaling the position to the range of positions and the intensity of each constituent in the chromatographic data is determined by scaling the position to the range of range of intensities. The position and intensity of each constituent in the chromatographic data is then presented in a graphical format.
A particularly useful application of these methods and processes is in the field of capillary electrophoresis. In capillary electrophoresis, materials to be separated based upon their size, e.g., nucleic acids, proteins, etc., are introduced into one end of a narrow bore capillary channel, which typically includes a separation matrix, e.g., a polymer solution or gel, disposed therein. Application of an electric field through the capillary channel then draws the sample through the channel. The presence of the polymer solution or gel, or alternatively, differential molecular charges of the macromolecular species, imparts a different mobility to the different macromolecular species in the sample, depending upon their size. Because a single thin channel is used for a given separation, typically only a single sample can be analyzed at any time, but channels could be utilized in parallel. However, a single capillary channel can serially analyze multiple samples effectively and this obviates the need for separately run ranges of standards. Instead, internal standards, e.g., of known molecular weight, typically are included with the sample materials, to provide a reference point against which the sample constituents or components may be compared. Typically, such standards will fall outside of the expected separation range for the sample constituents, e.g., have much larger or smaller molecular weights then the sample constituents. This permits the standards to be readily identified as the standards, and prevents them from interfering with the analysis of the sample constituents. Alternatively, differential labeling techniques may be used, whereby the standards may be distinguished from other constituents of the sample material by virtue of their incorporating a distinguishable label, e.g., having different light absorbing or emitting properties.
Separated species are generally detected at a single point along the length of the capillary channel as they move past that point. Typically, detection is carried out through the incorporation or association of a detectable labeling group with the various macromolecular species. The data from the detector is typically displayed as peaks of optical intensity as a function of time, e.g., as a chromatogram, for each sample analyzed. Analysis of additional samples is then carried out serially, e.g., one after another, in the same capillary system, giving rise to multiple separate plots of optical intensity peaks vs. time. Because these data are obtained from separate runs, with potentially varying conditions, these multiple plots make it very difficult to compare data from different samples.
In one aspect of the present invention, data obtained in the form of a typical chromatographic plot of intensity peaks are displayed as a series of bands of varying widths and intensities, in a vertical ladder-like format. Further, a user may toggle back and forth between the different display modes, e.g., chromatogram and gel-like displays, as well as manipulate of the data to permit optimal comparison and analysis of this data, e.g., normalization of data to standards, interpolation/extrapolation of data to characterize data from the different samples and different constituents of each sample.
A further understanding of the nature and advantages of the invention described herein may be realized by reference to the remaining portions of the specification and the attached drawings.